WASHINGTON — Using fungi to kill coca and other illegal drug crops, such as cannabis, would be a risky tactic, as there is not enough data about how to control these killer moulds and what effect they could have on people and the environment, according to a U.S. government study released on Wednesday.

The U.S. Congress asked scientists to look into whether some types of fungi, called mycoherbicides, could stem the flow of illicit drugs into the United States by killing the plants used to make cocaine, marijuana and opium.

But scientists from the National Research Council, one of the national academies of science that advises U.S. policymakers, said evidence about the fungi was sketchy and incomplete.

“There are too many unresolved questions regarding efficacy — whether they’ll really perform in real-time conditions, and whether they’ll be safe to non-target plants,” said Raghavan Charudattan, chair of the committee that prepared the report and professor emeritus in the University of Florida’s department of plant pathology.

“We did not see any data where a high level of control could be achieved,” he said.

Mycoherbicides are toxic fungi that have been used as an environmentally friendly alternative to chemical weedkillers. They can also be targeted to specific plants, and can reproduce themselves, staying in the soil for many years.

But using them on a large scale against illicit drugs has never been tested, Charudattan said. A fungus could kill anywhere from 10% to 60% of an infected drug crop. It could also fail completely because of too much rain or a drought.

Related

Available evidence also does not address the practical challenges of trying to infect drug crops abroad.

Farmers could easily sabotage any herbicide campaign by using fungicides to protect their crops or cultivate plants resistant to the fungi. Growers could also attack any low-flying aircraft used to spray their crops.

And it is unknown whether the fungi could morph into chemical compounds known as mycotoxins, which are harmful to people, Charudattan said.

Mycoherbicides could also only be used with the permission of a country’s government, which has proven a challenge in the past.

Colombia, the world’s largest producer of cocaine, refused to approve such fungi to kill its coca plants when the United States proposed it in 2000.

The U.S. government has pushed experimentation with fungal pesticides in Colombia and other parts of Latin America and Asia as a way to combat drug crops.

In the 1990s, the U.S. Department of Agriculture conducted research into the mycoherbicides as a replacement for the chemical fungicides that are sprayed from crop dusters on coca and heroin-poppy crops.

In the past, natural fungal epidemics have killed off poppy crops in Afghanistan and coca crops in Peru.

Congress required government scientists to further study mycoherbicides against illicit drugs as part of a funding bill for the White House drug czar’s office in 2006.